Meanwhile, in the offices of the planners for the Defense Advanced Research Projects Agency (DARPA), discussions were being held that would have a major influence on the work at Berkeley. One of DARPA's early successes had been to set up a nationwide computer network to link together all their major research centers. At that time, they were finding that many of the computers at these centers were reaching the end of their useful lifetime and had to be replaced. The heaviest cost of replacement was the porting of the research software to the new machines. In addition, many sites were unable to share their software because of the diversity of hardware and operating systems.

Choosing a single hardware vendor was impractical because of the widely varying computing needs of the research groups and the undesirability of depending on a single manufacturer. Thus, the planners at DARPA decided that the best solution was to unify at the operating systems level. After much discussion, Unix was chosen as a standard because of its proven portability.

In the fall of 1979, Bob Fabry responded to DARPA's interest in moving towards Unix by writing a proposal suggesting that Berkeley develop an enhanced version of 3BSD for the use of the DARPA community. Fabry took a copy of his proposal to a meeting of DARPA image processing and VLSI contractors, plus representatives from Bolt, Beranek, and Newman, the developers of the ARPAnet. There was some reservation whether Berkeley could produce a working system; however, the release of 3BSD in December 1979 assuaged most of the doubts.

With the increasingly good reputation of the 3BSD release to validate his claims, Bob Fabry was able to get an 18-month contract with DARPA beginning in April 1980. This contract was to add features needed by the DARPA contractors. Under the auspices of this contract, Bob Fabry sets up an organization which was christened the Computer Systems Research Group, or CSRG for short. He immediately hired Laura Tong to handle the project administration. Fabry turned his attention to finding a project leader to manage the software development. Fabry assumed that since Joy had just passed his Ph.D. qualifying examination, he would rather concentrate on completing his degree than take the software development position. But Joy had other plans. One night in early March he phoned Fabry at home to express interest in taking charge of the further development of Unix. Though surprised by the offer, Fabry took little time to agree.

The project started promptly. Tong set up a distribution system that could handle a higher volume of orders than Joy's previous distributions. Fabry managed to coordinate with Bob Guffy at AT&T and lawyers at the University of California to formally release Unix under terms agreeable to all. Joy incorporated Jim Kulp's job control, and added auto reboot, a 1K block file system, and support for the latest VAX machine, the VAX-11/750. By October 1980, a polished distribution that also included the Pascal compiler, the Franz Lisp system, and an enhanced mail handling system was released as 4BSD. During its nine-month lifetime, nearly 150 copies were shipped. The license arrangement was on a per-institution basis rather than a per machine basis; thus the distribution ran on about 500 machines.

With the increasingly wide distribution and visibility of Berkeley Unix, several critics began to emerge. David Kashtan at Stanford Research Institute wrote a paper describing the results of benchmarks he had run on both VMS and Berkeley Unix. These benchmarks showed severe performance problems with the Unix system for the VAX. Setting his future plans aside for several months, Joy systematically began tuning up the kernel. Within weeks he had a rebuttal paper written showing that Kashtan's benchmarks could be made to run as well on Unix as they could on VMS.

Rather than continue shipping 4BSD, the tuned-up system, with the addition of Robert Elz's auto configuration code, was released as 4.1BSD in June, 1981. Over its two- year lifetime about 400 distributions were shipped. The original intent had been to call it the 5BSD release; however, there were objections from AT&T that there would be customer confusion between their commercial Unix release, System V, and a Berkeley release named 5BSD. So, to resolve the issue, Berkeley agreed to change the naming scheme for future releases to stay at 4BSD and just increment the minor number.